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(No Model.)

C. E. CARPENTER. RHBOSTAT PLATE.

No. 492,758. Patented. Peb. 28, 1893l ATTORNEY.

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- U NTTED STATES PATENT OEEICE.

CHARLES E. CARPENTER, OF BRIDGEPORT, CONNECTICUT, ASSIGNOR TO THECARPENTER ENAMEL RHEOSTAT COMPANY, OF SAME PLACE.

RH EOSTAT-PLATE.

SPECIFICATION forming part of Letters Patent No. 492,758, dated February28, 1893.

Application filed October 27,. 1892 Serial No. 450,123 (No model.)

To all whom it may concern:

Be it known that I, CHARLES E. CARPENTER, a resident of the city ofBridgeport, county of Fairfield, and State of Connecticut, have inventeda new and useful Improvement in Resistance or Rheostat Plates, of whichthe following is a specication.

My invention relates to certain new and useful improvements in thatclass of resistance or rheostats described in my Letters Patent No.447,023, dated February 24, 1891, wherein the resistance or rheostatconsists of acoil or ribbon of Wire embedded in enamel or its equivalentwhich serves to attach said resistance to a base plate.

Heretofore it has been the practice to place the enamel and resistanceWire on a plane surface plate, but on account of the eXpansion of thewire, the enamel is liable to cleave from a plain surface plate.

One of the objects of my invention is to provide a surface plate, suchthat fora given amount of resistance Wire a greater amount of surface isprovided for adhesion of the enamel, and one Where the enamel shall beso distributed with relation to the plate and resistance Wire, that theenamel shall hold the Wire more firmly in position against displacement.

In the drawings Figure l is a plan View of the improved resistance, orrheostat, plate, and Fig. 2 an enlarged cross section thereof.

R is the resistance, which preferably consists of a wire, connected totwo or more terminals C, of any desirable form, which connect theresistance Wire with the electric current.

E is the enamel or its equivalent used for securing the restance wireto, but insulating the same from the base plate B, and which furtherserves to surround the Wire, and protect the same from chemical action.

` The base plate B isprovided on its surface with ribs or projections Afor the purpose hereinafter described. Between these ribs A are placedthe coils of resistance Wire which are then coated with enamel orequivalent material which may or may not lill the channels completely,and in some cases it is desirable to have the ribs or projections com-5o pletely covered by this insulation.

In the operation of apparatus in which the Wires are embedded in enamel,there are two expansions of the Wire viz;, diametrical and linear, whichoperate at right angles to each other, and both of which tend to crackor cleave the enamel from the surface plate. It will be readily seen byreference to Fig. 2 that where the Wires are enameled between ribs orprojections, as here shown, that it will 6o require a much greaterstrain to dislodge the enamel so placed, than if the ribs or projectionsdid not exist. As will be seen, the surface is here so formed thatportions of the surface are nearly at right angles to each other, andthe enamel in cleaving or separating from the base B must also separatefrom rib A as Well, or in other words, it must separate from the sidesand bottom of the channel or two or more surfaces of dierent angle 7o atthe same time. Another advantage of this construction in addition topreventing injury to the enamel by expansion of the wires, is in someapplications of this apparatus, notably electric railways, theseprojections serve t0 75 hold the enamel firmly to the surface of themetal against being loosened by continual jarring or vibration. The ribsalso serve to protect the enanmel from mechanical injury.

It is evident that modications may be A8o made of the exactconstruction, as here shown and described, without parting from thespirit of my invention, and my invention is calculated to comprehend allforms of the apparatus in which ribs or projections of any character areused for the purpose herein described.

What I claim, and desire to secure by Letters Patent, is-

1. A resistance, or rheostat, consisting` of a 9o base plate providedWith ribs or projections,

a layer of enamel between said ribs or projeetions anda conductor buriedin said enamel, substantially as described.

2. A resistance, or rheostat, having the eon- 9 5 duetor embedded inenamel Which is aiiixed t0 a base plate having ribs or projections for4. In a resistance plate having a support extending the surface to whichthe enamel which is covered by an insulating enamel, lo adheres,substantially as described. said enamel being divided into sections,sub- 3. In a resistance, or rheostat, havingr the stantially asdescribed.

5 conductor embedded in insulating materiale. CHARLES E. CARPENTER.

base-plate having projections forming an ex- NTitnesses: tended surfacefor the adhesion of the insu- HENRY B. DREW, lating material,substantially as described. A. L. EUGENE.

